Navigational control system for a robotic device

ABSTRACT

A navigational control system for altering movement activity of a robotic device operating in a defined working area, comprising a transmitting subsystem integrated in combination with the robotic device, the transmitting subsystem comprising means for emitting a number of directed beams, each directed beam having a predetermined emission pattern, and a receiving subsystem functioning as a base station that includes a navigation control algorithm that defines a predetermined triggering event for the navigational control system and a set of detection units positioned within the defined working area in a known spaced-apart relationship, the set of detection units being configured and operative to detect one or more of the directed beams emitted by the transmitting system; and wherein the receiving subsystem is configured and operative to process the one or more detected directed beams under the control of the navigational control algorithm to determine whether the predetermined triggering event has occurred, and, if the predetermined triggering event has occurred transmit a control signal to the robotic device, wherein reception of the control signal by the robotic device causes the robotic device to implement a prescribed conduct that alters the movement activity of the robotic device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application 11/682,642, filedMar. 6, 2007, which is a continuation of U.S. nonprovisional applicationSer. No. 11/341,111, filed Jan. 27, 2006, entitled “Navigational ControlSystem For A Robotic Device”, now issued U.S. Pat. No. 7,188,000, whichis a continuation of and is based upon and claims priority from U.S.nonprovisional application Ser. No. 10/661,835, filed Sep. 12, 2003,entitled “Navigational Control System For A Robotic Device” now issuedU.S. Pat. No. 7,024,278, which is based upon and claims priority fromU.S. provisional patent application Ser. No. 60/410,480, filed Sep. 13,2002, entitled “Beacon-Based Navigational System”.

This nonprovisional patent application is related to commonly-owned,co-pending U.S. nonprovisional patent application Ser. No. 10/056,804,filed 24 Jan. 2002, entitled METHOD AND SYSTEM FOR ROBOT LOCALIZATIONAND CONFINEMENT, U.S. nonprovisional patent application Ser. No.10/320,729, filed 16 Dec. 2002, entitled AUTONOMOUS FLOOR-CLEANINGDEVICE, U.S. nonprovisional patent application Ser. No. 10/167,851,filed 12 Jun. 2002, entitled METHOD AND SYSTEM FOR MULTI-MODE COVERAGEFOR AN AUTONOMOUS ROBOT, and U.S. nonprovisional continuation-in-partpatent application Ser. No. 10/453,202, filed 3 Jun. 2003, entitledROBOT OBSTACLE DETECTION SYSTEM, each of which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates generally to mobile robotic devices, andmore particularly, to a navigational control system for a robotic deviceoperating under the direction of a navigation control algorithm thattracks the movement activity of the robotic device and utilizes movementactivity to provide one or more control instructions to the roboticdevice, which in response thereto, implements a prescribed conduct,e.g., one or more basic maneuvers and/or behavioral patterns to increasethe coverage efficiency of such robotic devices for covering a definedworking area, e.g., sweeping, vacuuming a room, and/or performingresidential yard maintenance.

(2) Description of Related Prior Art

Robotic engineers have long worked on developing an effective method ofautonomous cleaning. This has led to the development of two separate anddistinct schemes for autonomous robotic devices: (1) deterministiccleaning; and (2) random cleaning.

In deterministic cleaning, where the cleaning rate equals the coveragerate and is, therefore, a more efficient cleaning method thanrandom-motion cleaning, the autonomous robotic device follows a definedpath, e.g., a boustrophedon path that is calculated to facilitatecomplete cleaning coverage of a given area while eliminating redundantcleaning. Deterministic cleaning requires that the robotic devicemaintain precise position knowledge at all times, as well as itsposition history (where it has been), which, in turn, requires asophisticated positioning system. A suitable positioning system—apositioning system suitably accurate for deterministic cleaning mightrely on scanning laser ranging systems, ultrasonic transducers, acarrier phase differential GPS, or other sophisticated methods—istypically prohibitively expensive and labor intensive, requiring aninvolved pre-setup to accommodate the unique conditions of each area tobe cleaned, e.g., room geometry, furniture locations. In addition,methods that rely on global positioning are typically incapacitated byfailure of any part of the positioning system.

One illustrative example of a highly sophisticated (and relativelyexpensive) robotic device for deterministic cleaning is the RoboScrubdevice built by Denning Mobile Robotics and Windsor Industries. TheRoboScrub device employs sonar and infrared detectors, bump sensors, anda high-precision laser navigation system to define the deterministiccleaning path. The navigation system employed with the RoboScrub devicerequires numerous large bar code targets to be set up in variousstrategic positions within the area to be cleaned, and effectiveoperation of the navigation system requires that at least four of suchtargets be visible simultaneously. This target accessibility requirementeffectively limits the use of the RoboScrub device to large unclutteredopen areas.

Other representative deterministic robotic devices are described in U.S.Pat. No. 5,650,702 (Azumi), U.S. Pat. No. 5,548,511 (Bancroft), U.S.Pat. No. 5,537,017 (Feiten et al.), U.S. Pat. No. 5,353,224 (Lee etal.), U.S. Pat. No. 4,700,427 (Knepper), and U.S. Pat. No. 4,119,900(Kreimnitz). These representative deterministic robotic devices arelikewise relatively expensive, require labor intensive pre-setup, and/orare effectively limited to large, uncluttered areas of simple geometricconfiguration (square, rectangular rooms with minimal (or no)furniture).

Due to the limitations and difficulties inherent in purely deterministiccleaning systems, some robotic devices rely on pseudo-deterministiccleaning schemes such as dead reckoning. Dead reckoning consists ofcontinually measuring the precise rotation of each drive wheel (e.g.,using optical shaft encoders) to continually calculate the currentposition of the robotic device, based upon a known starting point andorientation. In addition to the disadvantages of having to startcleaning operations from a fixed position with the robotic device in aspecified orientation, the drive wheels of dead reckoning roboticdevices are almost always subject to some degree of slippage, whichleads to errors in the calculation of current position. Accordingly,dead reckoning robotic devices are generally considered unreliable forcleaning operations of any great duration—resulting in intractablesystem neglect, i.e., areas of the surface to be cleaned are notcleaned. Other representative examples of pseudo-deterministic roboticdevices are described in U.S. Pat. No. 6,255,793 (Peless et al.) andU.S. Pat. No. 5,109,566 (Kobayashi et al.).

A robotic device operating in random motion, under the control of one ormore random-motion algorithms stored in the robotic device, representsthe other basic approach to cleaning operations using autonomous roboticdevices. The robotic device autonomously implement such random-motionalgorithm(s) in response to internal events, e.g., signals generated bya sensor system, elapse of a time period (random or predetermined). In atypical room without obstacles, a robotic device operating under thecontrol of a random-motion algorithm will provide acceptable cleaningcoverage given enough cleaning time. Compared to a robotic deviceoperating in a deterministic cleaning mode, a robotic device utilizing arandom-motion algorithm must operate for a longer period of time toachieve acceptable cleaning coverage. To have a high confidence that arandom-motion robotic device has cleaned 98% of an obstacle-free room,the random-motion robotic device must run approximately five timeslonger than a deterministic robotic device having similarly sizedcleaning mechanisms and moving at approximately the same speed.

However, an area to be cleaned that includes one or morerandomly-situated obstacles causes a marked increase in the running timefor a random-motion robotic device to effect 98% cleaning coverage.Therefore, while a random motion robotic device is a relativelyinexpensive means of cleaning a defined working area as contrasted to adeterministic robotic device, the random-motion robotic device requiresa significantly higher cleaning time.

A need exists to provide a deterministic component to a random-motionrobotic device to enhance the cleaning efficiency thereof to reduce therunning time for the random-motion robotic cleaning to achieve a 98%cleaning coverage.

BRIEF SUMMARY OF THE INVENTION

One object of the present invention is to provide a navigational controlsystem that enhances the cleaning efficiency of a robotic device byadding a deterministic component (in the form of a conduct prescribed bya navigation control algorithm) to the random motion of the roboticdevice generated by predetermined behavioral modes stored in the roboticdevice.

Another object of the present invention is to provide a navigationalcontrol unit operating under a navigation control algorithm thatincludes a predetermined triggering event that defines when theprescribed conduct will be implemented by the robotic device.

These and other objects of the present invention are achieved by meansof a navigational control system for deterministically altering movementactivity of a robotic device operating in a defined working area,comprising a transmitting subsystem integrated in combination with therobotic device, the transmitting subsystem comprising means for emittinga number of directed beams, each directed beam having a predeterminedemission pattern, and a receiving subsystem functioning as a basestation that includes a navigation control algorithm that defines apredetermined triggering event for the navigational control system and aset of detection units positioned within the defined working area, thedetection units being positioned in a known aspectual relationship withrespect to one another, the set of detection units being configured andoperative to detect one or more of the directed beams emitted by thetransmitting system; and wherein the receiving subsystem is configuredand operative to process the one or more detected directed beams underthe control of the navigational control algorithm to determine whetherthe predetermined triggering event has occurred, and, if thepredetermined triggering event has occurred transmit a control signal tothe robotic device, wherein reception of the control signal by therobotic device causes the robotic device to implement a prescribedconduct that deterministically alters the movement activity of therobotic device.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention and the attendantfeatures and advantages thereof can be had by reference to the followingdetailed description of the invention when considered in conjunctionwith the accompanying drawings wherein:

FIG. 1 is a top-view schematic of an exemplary robotic device havingparticular utility for use in the navigational control system accordingto the present invention.

FIG. 2 is an exemplary hardware block diagram for the robotic device ofFIG. 1.

FIG. 3 is a schematic depiction of a navigational control systemaccording to the present invention that comprises a transmittingsubsystem and a receiving subsystem.

FIG. 4 illustrates a polar tessellation of a defined working area inwhich a robotic device is operating.

FIG. 5A illustrates the operation of one preferred embodiment of atransmitting subsystem in synchronized operation with the receivingsubsystem of a preferred embodiment of the navigational control systemaccording to the present invention.

FIG. 5B illustrates the operation of the receiving subsystem insynchronized operation with the transmitting subsystem of FIG. 5A.

FIG. 5C illustrates the operation of another embodiment of atransmitting subsystem in synchronized operation with the receivingsubsystem of a preferred embodiment of the navigational control systemaccording to the present invention.

FIG. 5D illustrates the operation of the receiving subsystem insynchronized operation with the transmitting subsystem of FIG. 5C.

FIG. 6A illustrates one preferred embodiment of a navigational controlsystem according to the present invention wherein the transmittingsubsystem in integrated in combination with the robotic device and thereceiving system functions as a base station mounted against one wall ofa defined working area.

FIG. 6B illustrates the set of transmitting units comprising thetransmitting subsystem of the robotic device of FIG. 6A andrepresentative directed beams having a predetermined emission patterns.

FIG. 6C is a schematic illustration of a preferred embodiment of thereceiving subsystem of FIG. 6A.

FIG. 7 illustrates an exemplary embodiment of a navigational controlsystem according to the present invention wherein the receivingsubsystem is integrated in combination with the robotic device and thetransmitting subsystem has a distributed configuration.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings wherein like reference numerals identifycorresponding or similar elements throughout the several views, FIG. 1is a top-view schematic of an exemplary preferred embodiment of arobotic device 100 having particular utility in combination with anavigational control system 10 according to the present invention. FIG.2 is a block diagram of the hardware of the robot device 100 of FIG. 1.

The hardware and behavioral modes (coverage behaviors for cleaningoperations; escape behaviors for transitory movement patterns; andsafety behaviors for emergency conditions) of the robotic device 100,which is manufactured, distributed, and/or marketed by the iRobotCorporation of Burlington, Mass. under the ROOMBA trademark, are brieflydescribed in the following paragraphs to facilitate a more completeunderstanding of the navigational control system 10 of the presentinvention. Further details regarding the hardware and behavioral modesof the robotic device 100 can be found in commonly-owned, co-pendingU.S. nonprovisional patent application Ser. No. 10/167,851, filed 12Jun. 2002, entitled METHOD AND SYSTEM FOR MULTI-MODE COVERAGE FOR ANAUTONOMOUS ROBOT, and U.S. nonprovisional patent application Ser. No.10/320,729, filed 16 Dec. 2002, entitled AUTONOMOUS FLOOR-CLEANINGDEVICE.

In the following description of the robotic device 100, use of theterminology “forward”/“fore” refers to the primary direction of motion(forward) of the robotic device (see arrow identified by referencecharacter “FM” in FIG. 1). The fore/aft axis FA_(X) of the roboticdevice 100 coincides with the medial diameter of the robotic device 100that divides the robotic device 100 into generally symmetrical right andleft halves, which are defined as the dominant and non-dominant sides,respectively.

Robotic Device

The robotic device 100 has a generally cylindrical housinginfrastructure that includes a chassis 102 and an outer shell 104secured to the chassis 102 that define a structural envelope of minimalheight (to facilitate movement under furniture). The hardware comprisingthe robotic device 100 can be generally categorized as the functionalelements of a power system, a motive power system, a sensor system, acontrol module, a side brush assembly, or a self-adjusting cleaning headsystem, respectively, all of which are integrated in combination withthe housing infrastructure. In addition to such categorized hardware,the robotic device 100 further includes a forward bumper 106 having agenerally arcuate configuration and a nose-wheel assembly 108.

The forward bumper 106 (illustrated as a single component;alternatively, a two-segment component) is integrated in movablecombination with the chassis 102 (by means of displaceable supportmembers pairs) to extend outwardly therefrom. Whenever the roboticdevice 100 impacts an obstacle (e.g., wall, furniture) during movementthereof, the bumper 106 is displaced (compressed) towards the chassis102 and returns to its extended (operating) position when contact withthe obstacle is terminated.

The nose-wheel assembly 108 is mounted in biased combination with thechassis 102 so that the nose-wheel subassembly 108 is in a retractedposition (due to the weight of the robotic device 100) during cleaningoperations wherein it rotates freely over the surface being cleaned.When the nose-wheel subassembly 108 encounters a drop-off duringoperation (e.g., descending stairs, split-level floors), the nose-wheelassembly 108 is biased to an extended position.

The hardware of the power system, which provides the energy to power theelectrically-operated hardware of the robotic device 100, comprises arechargeable battery pack 110 (and associated conduction lines, notshown) that is integrated in combination with the chassis 102.

The motive power system provides the means that propels the roboticdevice 100 and operates the cleaning mechanisms, e.g., side brushassembly and the self-adjusting cleaning head system, during movement ofthe robotic device 100. The motive power system comprises left and rightmain drive wheel assemblies 112L, 112R, their associated independentelectric motors 114L, 114R, and electric motors 116, 118 for operationof the side brush assembly and the self-adjusting cleaning headsubsystem, respectively.

The main drive wheel assemblies 112L, 112R are independently mounted inbiased combination with the chassis 102 (for pivotal motion with respectthereto) at opposed ends of the transverse diameter (with respect to thefore-aft axis FA_(X)) of the robotic device 100 and are in a retractedposition (due to the weight of the robotic device 100) during operationthereof wherein the axes of rotation are approximately coplanar with thebottom of the chassis 102. If the robotic device 100 is removed from thesurface being cleaned, the main wheel assemblies 112L, 112R arepivotally-biased to an extended position wherein their axes of rotationare below the bottom plane of the chassis 102 (in this extended positionthe rechargeable battery pack 110 is automatically turned off by thecontrol module executing one of the safety behavioral modes).

The electric motors 114L, 114R are mechanically coupled to the maindrive wheel assemblies 112L, 112R, respectively, and independentlyoperated by control signals generated by the control module as aresponse to the implementation of a behavioral mode. Independentoperation of the electric motors 114L, 114R allows the main wheelassemblies 112L, 112R to be: (1) rotated at the same speed in the samedirection to propel the robotic device 100 in a straight line, forwardor aft; (2) differentially rotated (including the condition wherein onewheel assembly is not rotated) to effect a variety of right and/or leftturning patterns (over a spectrum of sharp to shallow turns) for therobotic device 100; and (3) rotated at the same speed in oppositedirections to cause the robotic device 100 to turn in place, i.e., “spinon a dime”, to provide an extensive repertoire of movement capabilityfor the robotic device 100.

The sensor system comprises a variety of different sensor units that areoperative to generate signals that control the behavioral modeoperations of the robotic device 100. The described robotic device 100includes obstacle detection units 120, cliff detection units 122, wheeldrop sensors 124, an obstacle-following unit 126, a virtual wallomnidirectional detector 128, stall-sensor units 130, and main wheelencoder units 132.

For the described embodiment, the obstacle (“bump”) detection units 120are IR break beam sensors mounted in combination with the displaceablesupport member pairs of the forward bumper 106. These detection units120 are operative to generate one or more signals indicating relativedisplacement between one or more support member pairs whenever therobotic device 100 impacts an obstacle such that the forward bumper 106is compressed. These signals are processed by the control module todetermine an approximate point of contact with the obstacle relative tothe fore-aft axis FA_(X) of the robotic device 100 (and the behavioralmode(s) to be implemented).

The cliff detection units 122 are mounted in combination with theforward bumper 106. Each cliff detection unit 122 comprises an IRemitter—detector pair configured and operative to establish a focalpoint such that radiation emitted downwardly by the emitter is reflectedfrom the surface being traversed and detected by the detector. Ifreflected radiation is not detected by the detector, i.e., a drop-off isencountered, the cliff detection unit 122 transmits a signal to thecontrol module (which causes one or more behavioral modes to beimplemented).

A wheel drop sensor 124 such as a contact switch is integrated incombination with each of the main drive wheel assemblies 112L, 112R andthe nose wheel assembly 108 and is operative to generate a signalwhenever any of the wheel assemblies is in an extended position, i.e.,not in contact with the surface being traversed, (which causes thecontrol module to implement one or more behavioral modes).

The obstacle-following unit 126 for the described embodiment is an IRemitter—detector pair mounted on the ‘dominant’ side (right hand side ofFIG. 1) of the robotic device 100. The emitter—detector pair is similarin configuration to the cliff detection units 112, but is positioned sothat the emitter emits radiation laterally from the dominant side of therobotic device 100. The unit 126 is operative to transmit a signal tothe control module whenever an obstacle is detected as a result ofradiation reflected from the obstacle and detected by the detector. Thecontrol module, in response to this signal, causes one or morebehavioral modes to be implemented.

A virtual wall detection system for use in conjunction with thedescribed embodiment of the robotic device 100 comprises anomnidirectional detector 128 mounted atop the outer shell 104 and astand-alone transmitting unit (not shown) that transmits anaxially-directed confinement beam. The stand-alone transmitting unit ispositioned so that the emitted confinement beam blocks an accessway to adefined working area, thereby restricting the robotic device 100 tooperations within the defined working area (e.g., in a doorway toconfine the robotic device 100 within a specific room to be cleaned).Upon detection of the confinement beam, the omnidirectional detector 128transmits a signal to the control module (which causes one or morebehavioral modes to be implemented to move the robotic device 100 awayfrom the confinement beam generated by the stand-alone transmittingunit).

A stall sensor unit 130 is integrated in combination with each electricmotor 114L, 114R, 116, 118 and operative to transmit a signal to thecontrol module when a change in current is detected in the associatedelectric motor (which is indicative of a dysfunctional condition in thecorresponding driven hardware). The control module is operative inresponse to such a signal to implement one or more behavioral modes.

An IR encoder unit 132 (see FIG. 2) is integrated in combination witheach main wheel assembly 112L, 112R and operative to detect the rotationof the corresponding wheel and transmit signals corresponding theretothe control module (wheel rotation can be used to provide an estimate ofdistance traveled for the robotic device 100).

The control module comprises the microprocessing unit 135 illustrated inFIG. 2 that includes I/O ports connected to the sensors and controllablehardware of the robotic device 100, a microcontroller, and ROM and RAMmemory. The I/O ports function as the interface between themicrocontroller and the sensor units and controllable hardware,transferring signals generated by the sensor units to themicrocontroller and transferring control (instruction) signals generatedby the microcontroller to the controllable hardware to implement aspecific behavioral mode.

The microcontroller is operative to execute instruction sets forprocessing sensor signals, implementing specific behavioral modes basedupon such processed signals, and generating control (instruction)signals for the controllable hardware based upon implemented behavioralmodes for the robotic device 100. The cleaning coverage and controlprograms for the robotic device 100 are stored in the ROM of themicroprocessing unit 135, which includes the behavioral modes, sensorprocessing algorithms, control signal generation algorithms and aprioritization algorithm for determining which behavioral mode or modesare to be given control of the robotic device 100. The RAM of themicroprocessing unit 135 is used to store the active state of therobotic device 100, including the ID of the behavioral mode(s) underwhich the robotic device 100 is currently being operated and thehardware commands associated therewith.

The side brush assembly 140 is configured and operative to entrainparticulates outside the periphery of the housing infrastructure and todirect such particulates towards the self-adjusting cleaning headsystem. The side brush assembly 140 provides the robotic device 100 withthe capability of cleaning surfaces adjacent to base-boards when therobotic device is operated in an Obstacle-Following behavioral mode. Asshown in FIG. 1, the side brush assembly 140 is preferably mounted incombination with the chassis 102 in the forward quadrant on the dominantside of the robotic device 100.

The self-adjusting cleaning head system 145 for the described roboticdevice 100 comprises a dual-stage brush assembly and a vacuum assembly,each of which is independently powered by an electric motor (referencenumeral 118 in FIG. 1 actually identifies two independent electricmotors—one for the brush assembly and one for the vacuum assembly). Thecleaning capability of the robotic device 100 is commonly characterizedin terms of the width of the cleaning head system 145 (see referencecharacter W in FIG. 1).

The dual-stage brush assembly and the inlet of the vacuum assembly areintegrated in combination with a deck structure, which is pivotallymounted in combination with the chassis 102 and operatively integratedwith the motor of the dual-stage brush assembly. In response to apredetermined reduction in rotational speed of the brush assembly motor,the brush assembly motor provides the motive force to pivot the deckstructure with respect to the chassis 102. The pivoting deck structureprovides the self adjusting capability for the cleaning head assembly145, which allows the robotic device 100 to readily transition betweendisparate surfaces during cleaning operations, e.g., carpeted surface tobare surface or vice versa, without hanging up.

The dual-stage brush assembly comprises asymmetric, counter-rotatingbrushes that are positioned (forward of the inlet of the vacuumassembly), configured and operative to direct particulate debris into aremovable dust cartridge (not shown). The positioning, configuration,and operation of the brush assembly concomitantly directs particulatedebris towards the inlet of the vacuum assembly such that particulatesthat are not swept up by the dual-stage brush assembly can besubsequently ingested by the vacuum assembly as a result of movement ofthe robotic device 100.

Operation of the vacuum assembly independently of the self-adjustablebrush assembly allows the vacuum assembly to generate and maintain ahigher vacuum force using a battery-power source than would be possibleif the vacuum assembly were operated in dependence with the brushassembly.

Behavioral Modes for Robotic Device

The robotic device 100 uses a variety of behavioral modes to effectivelyclean a defined working area where behavioral modes are layers ofcontrol systems that can be operated in parallel. The microprocessorunit 135 is operative to execute a prioritized arbitration scheme toidentify and implement one or more dominant behavioral modes for anygiven scenario based upon inputs from the sensor system.

The behavioral modes for the described robotic device 100 can becharacterized as: (1) coverage behavioral modes; (2) escape behavioralmodes; and (3) safety behavioral modes. Coverage behavioral modes areprimarily designed to allow the robotic device 100 to perform itscleaning operations in an efficient and effective manner and the escapeand safety behavioral modes are priority behavioral modes implementedwhen a signal from the sensor system indicates that normal operation ofthe robotic device 100 is impaired, e.g., obstacle encountered, or islikely to be impaired, e.g., drop-off detected.

Representative and illustrative coverage behavioral (cleaning) modes forthe robotic device 100 include: (1) a Spot Coverage pattern; (2) anObstacle-Following (or Edge-Cleaning) Coverage pattern, and (3) a RoomCoverage pattern. The Spot Coverage pattern causes the robotic device100 to clean a limited area within the defined working area, e.g., ahigh-traffic area. In a preferred embodiment the Spot Coverage patternis implemented by means of a spiral algorithm (but other types ofself-bounded area algorithms, e.g., polygonal, can be used). The spiralalgorithm, which causes outward spiraling (preferred) or inwardspiraling movement of the robotic device 100, is implemented by controlsignals from the microprocessing unit 135 to the main wheel assemblies112L, 112R to change the turn radius/radii thereof as a function of time(thereby increasing/decreasing the spiral movement pattern of therobotic device 100).

The robotic device 100 is operated in the Spot Coverage pattern for apredetermined or random period of time, for a predetermined or randomdistance (e.g., a maximum spiral distance) and/or until the occurrenceof a specified event, e.g., activation of one or more of the obstacledetection units 120 (collectively a transition condition). Once atransition condition occurs, the robotic device 100 can implement ortransition to a different behavioral mode, e.g., a Straight Linebehavioral mode (in a preferred embodiment of the robotic device 100,the Straight Line behavioral mode is a low priority, default behaviorthat propels the robot in an approximately straight line at a presetvelocity of approximately 0.306 m/s) or a Bounce behavioral mode incombination with a Straight Line behavioral mode.

If the transition condition is the result of the robotic device 100encountering an obstacle, the robotic device 100 can take other actionsin lieu of transitioning to a different behavioral mode. The roboticdevice 100 can momentarily implement a behavioral mode to avoid orescape the obstacle and resume operation under control of the spiralalgorithm (i.e., continue spiraling in the same direction).Alternatively, the robotic device 100 can momentarily implement abehavioral mode to avoid or escape the obstacle and resume operationunder control of the spiral algorithm (but in the oppositedirection—reflective spiraling).

The Obstacle-Following Coverage pattern causes the robotic device 100 toclean the perimeter of the defined working area, e.g., a room bounded bywalls, and/or the perimeter of an obstacle (e.g., furniture) within thedefined working area. Preferably the robotic device 100 utilizesobstacle-following unit 126 to continuously maintain its position withrespect to an obstacle, e.g., wall, furniture, so that the motion of therobotic device 100 causes it to travel adjacent to and concomitantlyclean along the perimeter of the obstacle. Different embodiments of theobstacle-following unit 126 can be used to implement theObstacle-Following behavioral pattern.

In a first embodiment, the obstacle-following unit 126 is operated todetect the presence or absence of the obstacle. In an alternativeembodiment, the obstacle-following unit 126 is operated to detect anobstacle and then maintain a predetermined distance between the obstacleand the robotic device 100. In the first embodiment, the microprocessingunit 135 is operative, in response to signals from theobstacle-following unit, to implement small CW or CCW turns to maintainits position with respect to the obstacle. The robotic device 100implements a small CW when the robotic device 100 transitions fromobstacle detection to non-detection (reflection to non-reflection) or toimplement a small CCW turn when the robotic device 100 transitions fromnon-detection to detection (non-reflection to reflection). Similarturning behaviors are implemented by the robotic device 100 to maintainthe predetermined distance from the obstacle.

The robotic device 100 is operated in the Obstacle-Following behavioralmode for a predetermined or random period of time, for a predeterminedor random distance (e.g., a maximum or minimum distance) and/or untilthe occurrence of a specified event, e.g., activation of one or more ofthe obstacle detection units 120 a predetermined number of times(collectively a transition condition). In certain embodiments, themicroprocessor 135 will cause the robotic device to implement an Alignbehavioral mode upon activation of the obstacle-detection units 120 inthe Obstacle-Following behavioral mode wherein the implements a minimumangle CCW turn to align the robotic device 100 with the obstacle.

The Room Coverage pattern can be used by the robotic device 100 to cleanany defined working area that is bounded by walls, stairs, obstacles orother barriers (e.g., a virtual wall unit). A preferred embodiment forthe Room Coverage pattern comprises the Random-Bounce behavioral mode incombination with the Straight Line behavioral mode. Initially, therobotic device 100 travels under control of the Straight-Line behavioralmode, i.e., straight-line algorithm (main drive wheel assemblies 112L,112R operating at the same rotational speed in the same direction) untilan obstacle is encountered. Upon activation of one or more of theobstacle detection units 120, the microprocessing unit 135 is operativeto compute an acceptable range of new directions based upon the obstacledetection unit(s) 126 activated. The microprocessing unit 135 selects anew heading from within the acceptable range and implements a CW or CCWturn to achieve the new heading with minimal movement. In someembodiments, the new turn heading may be followed by forward movement toincrease the cleaning efficiency of the robotic device 100. The newheading may be randomly selected across the acceptable range ofheadings, or based upon some statistical selection scheme, e.g.,Gaussian distribution. In other embodiments of the Room Coveragebehavioral mode, the microprocessing unit 135 can be programmed tochange headings randomly or at predetermined times, without input fromthe sensor system.

The robotic device 100 is operated in the Room Coverage behavioral modefor a predetermined or random period of time, for a predetermined orrandom distance (e.g., a maximum or minimum distance) and/or until theoccurrence of a specified event, e.g., activation of theobstacle-detection units 120 a predetermined number of times(collectively a transition condition).

A preferred embodiment of the robotic device 100 includes four escapebehavioral modes: a Turn behavioral mode, an Edge behavioral mode, aWheel Drop behavioral mode, and a Slow behavioral mode. One skilled inthe art will appreciate that other behavioral modes can be utilized bythe robotic device 100. One or more of these behavioral modes may beimplemented, for example, in response to a current rise in one of theelectric motors 116, 118 of the side brush assembly 140 or dual-stagebrush assembly above a low or high stall threshold, forward bumper 106in compressed position for determined time period, detection of awheel-drop event.

In the Turn behavioral mode, the robotic device 100 turns in place in arandom direction, starting at higher velocity (e.g., twice normalturning velocity) and decreasing to a lower velocity (one-half normalturning velocity), i.e., small panic turns and large panic turns,respectively. Low panic turns are preferably in the range of 45° to 90°,large panic turns are preferably in the range of 90° to 270°. The Turnbehavioral mode prevents the robotic device 100 from becoming stuck onroom impediments, e.g., high spot in carpet, ramped lamp base, frombecoming stuck under room impediments, e.g., under a sofa, or frombecoming trapped in a confined area.

In the Edge behavioral mode follows the edge of an obstacle unit it hasturned through a predetermined number of degrees, e.g., 60°, withoutactivation of any of the obstacle detection units 120, or until therobotic device has turned through a predetermined number of degrees,e.g., 170°, since initiation of the Edge behavioral mode. The Edgebehavioral mode allows the robotic device 100 to move through thesmallest possible openings to escape from confined areas.

In the Wheel Drop behavioral mode, the microprocessor 135 reverses thedirection of the main wheel drive assemblies 112L, 112R momentarily,then stops them. If the activated wheel drop sensor 124 deactivateswithin a predetermined time, the microprocessor 135 then reimplementsthe behavioral mode that was being executed prior to the activation ofthe wheel drop sensor 124.

In response to certain events, e.g., activation of a wheel drop sensor124 or a cliff detector 122, the Slow behavioral mode is implemented toslowed down the robotic device 100 for a predetermined distance and thenramped back up to its normal operating speed.

When a safety condition is detected by the sensor subsystem, e.g., aseries of brush or wheel stalls that cause the corresponding electricmotors to be temporarily cycled off, wheel drop sensor 124 or a cliffdetection sensor 122 activated for greater that a predetermined periodof time, the robotic device 100 is generally cycled to an off state. Inaddition, an audible alarm may be generated.

The foregoing description of behavioral modes for the robotic device 100are intended to be representative of the types of operating modes thatcan be implemented by the robotic device 100. One skilled in the artwill appreciate that the behavioral modes described above can beimplemented in other combinations and/or circumstances.

Navigational Control System

FIG. 3 is a schematic representation of a navigational control system 10according to the present invention for use in combination with a roboticdevice 100 to enhance the cleaning efficiency thereof by adding adeterministic component (in the form of a control signal that remotelycontrols the movement of the robotic device 100) to the motionalgorithms, including random motion, autonomously implemented by therobotic device 100. The navigational control system 10 comprises atransmitting subsystem 12 and a receiving subsystem 20 operating underthe direction of a navigation control algorithm. The navigation controlalgorithm includes a definition of a predetermined triggering event. Thespecific features and characteristics of the transmitting subsystem 12and the receiving subsystem 20 depend upon whether the particularsubsystem is integrated in combination with the robotic device 100 orfunctions as a “base station” for the navigational control system 10.

Broadly described, the navigational control system 10 according to thepresent invention is operative, under the direction of the navigationcontrol algorithm, to monitor the movement activity of the roboticdevice 100 within the defined working area. In one preferred embodiment,the monitored movement activity is defined in terms of the “positionhistory” of the robotic device 100 as described in further detail below.In another preferred embodiment, the monitored movement activity isdefined in terms of the “instantaneous position” of the robotic device100 as defined in further detail below.

The predetermined triggering event is a specific occurrence or conditionin the movement activity of the robotic device 100. Upon the realizationof the predetermined triggering event, the navigational control system10 is operative to generate and communicate a control signal to therobotic device 100. In response to the control signal, the roboticdevice 100 is operative to implement or execute a conduct prescribed bythe control signal, i.e., the prescribed conduct. This prescribedconduct represents a deterministic component of the movement activity ofthe robotic device 100.

In the preferred embodiment of the navigational control system 10 basedupon position history, the system 10 is configured and operative tocreate a “tessellation” of any defined working area where the roboticdevice 100 is to be operated, e.g., a room to be cleaned. Tessellate isused herein in the sense that the defined working area is segmented intoa set of individual cells, which may or may not be of equal size. Forexample, FIG. 4 exemplarily illustrates the polar tessellation of adefined working area into a set of individual cells C (referencecharacters BS_(T) identify the “base station”) of unequal size. Theposition of each cell C (in terms of its center) is identified in termsof polar coordinates (r, θ) referenced to the base station BS_(T) as theorigin (0, 0). A grid map of the cells C comprising the defined workingarea is stored in memory of the navigation control system 10. Oneskilled in the art will appreciate that other coordinate systems, e.g.,a planar Cartesian coordinate system, can be used by the navigationalcontrol system 10 to define the position of individual cells C withinthe predetermined working area.

Preferably, the navigational control system 10 is operative to definethe size the individual cells C so that the length and width dimensionsof an individual cell C are no larger than one-half the width (W) of thecleaning head system 145 of the robotic device 100 (see FIG. 1 andcorresponding discussion above).

The navigational control system 10 is operative to generate a positionhistory of the robotic device 100 within the defined working area interms of such individual cells C (to minimize the memory requirementsfor storage of position history). The position history comprises a setof discrete, instantaneous positions (in terms of individual cells C) ofthe robotic device 100 over a time interval where the time interval is avariable that depends upon the “triggering condition” of the navigationcontrol algorithm implemented by the navigational control system 10.

Each discrete instantaneous position of the robotic device 100 isdetermined by operating the transmitting subsystem 12 to emit a set ofdirectional beams and operating the receiving subsystem 20 to detect oneor more of such directional beams and process a signal parameter of thedetected beam(s) to determine an absolute bearing parameter and adistance parameter between the transmitting subsystem 12 and thereceiving subsystem 20 at a point in time. Each pair of bearing,distance parameters establishes a discrete instantaneous position forthe robotic device 100. For the preferred ‘position history’ embodiment,the navigational control system 10 is operative to correlate eachdiscrete instantaneous position to one individual cell C of the gridmap. A set of bearing and position pairs, i.e., a set of instantaneouspositions, over a time interval defines a set of cells C, which areidentified in the receiving subsystem 20 as the position history of therobotic device 100 for the time interval.

In the preferred embodiment of the navigational control system 10 basedupon the instantaneous position, the system 10 processes each discreteinstantaneous position as it is established, under the control of thenavigation control algorithm, to determine whether such discreteinstantaneous position is the predetermined triggering event defined bythe navigation control algorithm.

In an advanced embodiment of the navigational control system 10, thesystem 10 is additionally configured and operative to determine a travelvector (indicating the direction of motion of the robotic device 100within an individual cell C or at the discrete instantaneous position)at each point in time. These travel vectors may be stored in memory inconjunction with the corresponding cells C as a component of theposition history of the robotic device 100.

The navigational control system 10 according to the present invention isfurther operative, under direction of the navigational controlalgorithm, to generate and communicate a control signal to the roboticdevice 100 whenever the navigational control system 100 realizes thepredetermined triggering event. In response to any such control signal,the robotic device 100 is configured and operative to initiate aprescribed conduct. The prescribed conduct comprises the deterministiccomponent added to the random motion movement activity of the roboticdevice 100 by means of the navigational control system 10 according tothe present invention.

In one preferred embodiment of the invention, the prescribed conduct ofthe robotic device 100 comprises one or more basic maneuvers such as CWand CCW turns, forward or aft (straight line) movement, slow down, speedup, and stop. The CW and/or CCW turns can be implemented using theturning techniques of the robotic device 100 described above, and theturn angles can be, for example, over a 360° spectrum at predeterminedintervals, e.g., 5° or 10°. Alternatively, or in addition to, the CWand/or CCW turns can be to a specified azimuthal heading (referenced tothe base station as the origin) where the navigational control system 10is configured and operative so that the travel vector is a determinablevariable. Of these basic maneuvers, forward (straight line) movement istypically the default maneuver that the robotic device 100 automaticallyreverts to (implements) once one or more of the other basic maneuvershas been completed.

In another preferred embodiment of the invention, the prescribed conductof the robotic device 100 comprises one or more of the behavioral modesdescribed herein. In yet a further preferred embodiment of theinvention, the prescribed conduct of the robotic device 100 comprises acombination of the basic maneuvers and the behavioral modes describedherein.

The transmitting subsystem 12 is operative to transmit a number ofdirected beams having a predetermined emission pattern along a specificpropagation axis. Preferably, the directed beams are planar, i.e.,substantially parallel to the surface of the defined working area.

In preferred embodiments of the navigational control system 10 accordingto the present invention, the transmitting subsystem 12 is integrated incombination with the robotic device 100. The transmitting subsystem 12is configured and operative to functionally emulate an omnidirectionaltransmission source with respect to the defined working area, i.e., byemitting a plurality of directed beams that cover the defined workingarea. For these preferred embodiments, the robotic device 100 furtherincludes a receiver unit 16 (see FIG. 3) configured and operative toreceive control signals from the receiving subsystem 20 (see discussionbelow regarding the transmitting unit 32 of the receiving subsystem 20).While the receiver unit 16 is depicted as a dedicated receiving unit forthe control signals, it is preferable that the omnidirectional detector128 (of the virtual wall detection system) described above be adapted todetect and process such control signals.

In one preferred embodiment, the transmitting subsystem 12 comprises aconventional mechanical sweeping transmitter, e.g., a laser, that isintegrated in combination with a high point of the housinginfrastructure of the robotic device 100 so that none of the structuralfeatures of the robotic device 100 interfere with the operation thereof.The mechanical sweeping transmitter is configured and operative to emitthe plurality of directed beams while concomitantly redirecting(mechanically sweeping) the transmitting element so that each directedbeam has a different propagation axis. Other features andcharacteristics of the mechanical sweeping transmitter are describedbelow in terms of individual transmitting units 14 _(N) for ease ofdescription.

Another preferred embodiment of the transmitting subsystem 12 comprisesa set of transmitting units 14 _(N), where N is an integer defining thenumber of individual transmitting units comprising the set for thenavigational control system 10, that are integrated in combination withthe robotic device 100 about the periphery of its housinginfrastructure. Each transmitting unit 14N is configured and operativeto emit a directed beam having a predetermined emission pattern along aspecific propagation axis. Preferably, the transmitting subsystem 12 isconfigured and operative so that the emitted directed beams are planar.

In a basic embodiment of the transmitting subsystem 12, the transmittingunits 14 _(N) are fungible/interchangeable, each operating to emit adirected beam at a common operating frequency. Preferably, the commonoperating frequency for the transmitting units 14 _(N) lies in theinfrared range, i.e., about 750 nm to about 1.4×10⁴ nm, preferably about880 nm to about 980 nm, although one skilled in the art will appreciatethat other wavelengths, e.g., in the radio frequency range, microwavefrequency range, can be used in the practice of the navigational controlsystem 10 of the present invention.

Preferably, the common operating frequency directed beams emitted by thetransmitting units 14 _(N) are periodically modulated, e.g., at 10 KHzfor 50 msec, off for 300 msec. Modulation of the directed beamsfacilitates detection thereof by the receiving subsystem 20, i.e., thereceiving subsystem 20 is able to readily discriminate between modulateddirected beams emitted by the transmitting subsystem 12 and any otherelectromagnetic radiation sources that may be active in the definedworking area, e.g., television remote control units, wireless computerkeyboards, microwaves, ambient radiation such as sunlight. For the basicembodiment, it is also preferable that the transmitting units 14 _(N) besequentially operated so that any transmitting unit 14 _(N) is cycled onfor a predetermined period of time and then cycled off, the next(adjacent) transmitting unit 14 _(N) is then cycled on for thepredetermined period of time and cycled off, and so forth. Operating thetransmitting subsystem 12 in the foregoing manner, i.e., modulation ofthe directed beam, cycling transmitting units 14 _(N) on/offsequentially, minimizes the power requirements of the transmittingsubsystem 12 and reduces spurious noise/collateral energy that couldadversely impact the functioning of the navigational control system 10.

Ordinarily, a navigational control system 10 employing the basicembodiment of the transmitting subsystem 12, i.e., all transmittingunits 14 _(N) are interchangeable—emitting directed beams at a commonoperating frequency, cannot be used to determine travel vectors for therobotic device 100 because the receiving subsystem 20 cannotdifferentiate between directed beams emitted by the transmitting units14 _(N) and therefore cannot identify any particular transmitting unit14 _(N). However, the inventors have developed two innovative ways oftransmitting and processing directed beams emitted by a transmittingsubsystem 12 comprised of interchangeable transmitting units 14N so thatthe receiving subsystem 20 can individually identify a specificinterchangeable transmitting unit 14N, and, based upon suchidentification, establish a travel vector for the robotic device 100.

Accordingly, in one enhanced version of the basic embodiment of thetransmitting subsystem 12, interchangeable transmitting units 14N areoperated in a predetermined manner that allows the receiving subsystem20 to process detected directed beams to identify the directed beamhaving the highest signal strength, which, in turn, allows the receivingsubsystem 20 to identify the interchangeable transmitting unit 14 _(N)that emitted such directed beam. This, in turn, allows the receivingsubsystem 20 to determine the orientation and, hence the travel vector,of the robotic device 100.

Referring to FIG. 5A, the transmitting subsystem 12 is first cycled onso that all transmitting units 14 _(N) emit directed beams for apredetermined synchronization period, as identified by referencecharacter t_(SY), and then cycled off. The receiver subsystem 20 isoperative to detect and process one or more of the directed beamsemitted by the transmitting units 14 _(N) and identify the predeterminedsynchronization period t_(SY) of the transmitting subsystem 12. Thisidentification allows the receiving subsystem 20 to synchronizeoperations between the transmitting subsystem 12 and the receivingsubsystem 20 by initializing a timing sequence at the end of thepredetermined synchronization period t_(SY) (reference character t₀identifies the initialization of the timing sequence in FIG. 5A).

The transmitting subsystem 12 is further operative so that individualtransmitting unit 14 _(N) are sequentially cycled on and off atpredetermined times with respect to the timing sequence initializationt_(o) established by the receiving subsystem 20. For example, withrespect to FIG. 5A, which illustrates a transmitting subsystem 12comprising four transmitting units 14 _(N) (arbitrarily identified asthe first transmitting unit 14 ₁, the second transmitting unit 14 ₂, thethird transmitting unit 14 ₃, and the fourth transmitting unit 14 ₄),the transmitting subsystem 12 is configured and operative so that eachof the transmitting units 14 ₁, 14 ₂, 14 ₃, 14 ₄ is sequentially cycledon to emit a directed beam that transitions from a zero (0) signalstrength to a peak signal strength to a zero (0) signal strength andthen cycled off (a saw-tooth transition pattern is exemplarilyillustrated in FIG. 5A—one skilled in the art will appreciate that othertypes of signal strength transition patterns can be used in the practiceof the invention described herein, e.g., a ramped signal strength).

That is, the first transmitting unit 14 ₁ is cycled on and transitionsto a peak signal strength at time t₁. The second transmitting unit 14 ₂is cycled on as the directed beam from the first transmitting unit 14 ₁achieves its peak signal strength at time t₁. The second transmittingunit 14 ₂ transitions to a peak signal strength at time t₂, at whichpoint the first transmitting unit 14 ₁ has transitioned to a zero (0)signal strength and is cycled off. The third transmitting unit 14 ₃ iscycled on as the directed beam from the second transmitting unit 14 ₂achieves its peak signal strength at time t₂. The foregoing operatingpattern is repeated for the second, third, and fourth transmitting units14 ₂, 14 ₃, 14 ₄, as applicable, so that at time t₃ the secondtransmitting unit 14 ₂ is cycled off, the directed beam emitted by thethird transmitting unit 14 ₃ has achieved its peak signal strength, andthe fourth transmitting unit 14 ₄ is cycled on; and at time t₄ the thirdtransmitting unit 14 ₃ is cycled off and the directed beam emitted bythe fourth transmitting unit 14 ₄ has achieved its peak strength. Thetransmitting subsystem 12 is operative to repeat the above-describedsynchronization—sequential transmission procedure during operation ofthe navigational control system 12 according to the present invention.

In another enhanced version of the basic embodiment of the transmittingsubsystem 12, interchangeable transmitting units 14N are operated in adifferent predetermined manner that allows the receiving subsystem 20 toprocess detected directed beams to identify the directed beam having thehighest signal strength, which, in turn, allows the receiving subsystem20 to identify the interchangeable transmitting unit 14 _(N) thatemitted such directed beam. This, in turn, allows the receivingsubsystem 20 to determine the orientation and, hence the travel vector,of the robotic device 100.

Referring to FIG. 5C, the transmitting subsystem 12 is first cycled onso that all transmitting units 14 _(N) emit directed beams for apredetermined synchronization period, as identified by referencecharacter t₁₂, and then cycled off. The receiver subsystem 20 isoperative to detect and process one or more of the directed beamsemitted by the transmitting units 14 _(N) and identify the predeterminedsynchronization period t₁₂ of the transmitting subsystem 12. Thisidentification allows the receiving subsystem 20 to synchronizeoperations between the transmitting subsystem 12 and the receivingsubsystem 20 by initializing a timing sequence at the end of thepredetermined synchronization period t_(SY) (reference character t_(o)identifies the initialization of the timing sequence in FIG. 5A).

The transmitting subsystem 12 is further operative so that individualtransmitting unit 14 _(N) are sequentially cycled on and off atpredetermined times with respect to the timing sequence initializationt_(o) established by the receiving subsystem 20. For example, withrespect to FIG. 5C, which illustrates a transmitting subsystem 12comprising four transmitting units 14 _(N) (arbitrarily identified asthe first transmitting unit 14 ₁, the second transmitting unit 14 ₂, thethird transmitting unit 14 ₃, and the fourth transmitting unit 14 ₄),the transmitting subsystem 12 is configured and operative so that eachof the transmitting units 14 ₁, 14 ₂, 14 ₃, 14 ₄ is sequentially cycledon to emit a pulsed directed beam have a predetermined pulse width P₁,P₂, P₃, P₄, respectively, at a predetermined signal strength, and thencycled off.

That is, the first transmitting unit 14 ₁ is cycled on at t₁₁ (where thefirst “1” identifies the transmitting unit number and the second “1”indicates that the transmitting unit is cycled on) and cycled off at t₁₂(where the “2” indicates that the transmitting unit is cycled off). In asimilar manner, the second transmitting unit 14 ₂ is cycled on at t₂₁and cycled off at t₂₂, the third transmitting unit 14 ₃ is cycled on att₃₁ and cycled off at t₃₂, and fourth transmitting units 14 ₄ is cycledon at t₄₁ and cycled off at t₄₂. The transmitting subsystem 12 isoperative to repeat the above-described synchronization—sequentialtransmission procedure during operation of the navigational controlsystem 12 according to the present invention.

In a more sophisticated embodiment of the transmitting subsystem 12, thetransmitting units 14 _(N) are discrete and identifiable, eachtransmitting unit 14 _(N) operating at a unique operating frequency toemit a directed beam (which is preferably planar with respect to thesurface of the defined working area) having a predetermined emissionpattern along a specific propagation axis. These operating frequenciesare also preferably modulated to facilitate detection thereof by thereceiving subsystem 20 in an environment where other electromagneticradiation sources are operating. Since each directed beam is readily anduniquely identifiable, the receiving subsystem 20 can process detecteddirected beams in a conventional manner to derive not only the absolutebearing and to the robotic device 100, but also the travel vector forthe robotic device 10 at any particular time.

The receiving subsystem 20 of the navigational control system 10according to the present invention comprises a processing unit 22 thatincludes a microprocessor 24, a signal processing unit 26, a memorymodule 28, and a set of detection units 30 _(M). Additionally, thereceiving subsystem 20 can also include a transmitting unit 32 for thosepreferred embodiments of the navigational control system 10 wherein thereceiving subsystem 20 is operated or functions as the base station forthe navigational control system 10.

The memory module 28 comprises RAM 28A and ROM 28B. Data relating to thecurrent operation of the robotic device 100 within the defined workingarea is stored in the RAM 28A. Such current operational data can includethe grid map of cells C defining the defined working area and theposition history of the robotic device 100 within the defined workingarea for the ‘position history’ embodiment of the navigational controlsystem 10. Stored in the ROM 28B are one or more navigation controlalgorithms for the navigational control system 10, a set of one or morecontrol signals associated with each navigation control algorithm, and asignal processing algorithm for converting signals generated by thesignal processing unit 26 to one or more sets of instantaneous positionparameters, i.e., a bearing, distance pair (and travel vector, ifapplicable). For the ‘position history’ embodiment of the system 10, aset of instantaneous position parameters that define the positionhistory of the robotic device 100, which are correlated with the gridmap to identify the cells C comprising the position history.

The terminology “navigation control algorithm” as used hereinencompasses a set of instructions that: (a) define how the positionhistory or instantaneous position is used by the navigational controlsystem 10 (e.g., counting and comparing cells visited, a true-falsedetermination for cells visited, true-false determination whether thepredetermined triggering event has occurred); (b) defines the triggeringevent or events associated with the use of the position history or theinstantaneous position; and (c) identifies the control signal(s) to beimplemented when the triggering event is realized. For example, in onerepresentative navigation control algorithm for the ‘position history’embodiment of the navigational control system 10 according to thepresent invention, the microprocessor 24 is operative to count and storethe number of visits to each cell and to compute the total number ofvisits to cells contiguous to (neighboring) each such visited cell (cellcounting). The microprocessor 24 is further operative to compare thetotal number of neighboring-cell visits as each cell is visited to athreshold value (see, e.g., FIG. 4 wherein “C_(V)” identifies a visitedcell and “C_(C)” identifies the eight (8) cells contiguous to thevisited cell C_(V)). If the total number of neighboring-visits (e.g.,fifteen (15) in the example of FIG. 4) for any visited cell is below thethreshold number (the triggering event), the microprocessor 24 isoperative to cause a control signal to be communicated to the roboticdevice 100. The control signal causes the robotic device 100 toimplement one or more behavioral modes specified by the control signal,e.g., a Spot Coverage pattern as described above.

In another representative navigation control algorithm for the ‘positionhistory’ embodiment of the navigational control system 10 of the presentinvention, one or more cells in the stored grid map are pre-identified(i.e., prior to operating the robotic device 100) as “hot spots” in thedefined working area. As the robotic device 100 visits any particularcell C, the microprocessor 24 is operative to determine whether thevisited cell has been identified as a “hot spot” (true-falsedetermination). If the microprocessor 24 determines that the visitedcell C is a “hot spot” (triggering event), the microprocessor 24 isoperative to cause a control signal to be communicated to the roboticdevice 100 via the control signal transmitting unit 32. Reception of thecontrol signal causes the robotic device 100 to implement the prescribedconduct specified by the control signal, e.g., one or more of the basicmaneuvers described above and/or a Spot Coverage pattern orObstacle-Following behavioral mode as described above.

The foregoing representative examples of navigation control algorithmsfor the ‘position history’ embodiment of the navigational control system10 according to the present invention are implemented without knowledgeof the travel vector of the robotic device 100, i.e., based solely uponthe identification of visited cells by means of the bearing, distanceparameters derived by the receiving subsystem 20. Another representativeexample of a navigation control algorithm for the ‘position history’embodiment of the navigation control system 10 of the present inventionutilizes the travel vector as an element of the position history inissuing a control signal.

The microprocessor 24 is operative to count and store the number oftimes a cell has been visited (cell counting) and further operative tocompare this number to the number of times each contiguous (orneighboring) cell has been visited. For this navigation controlalgorithm, the triggering event is a numerical differential between thenumber of visits to the currently-visited cell number and the number ofvisits to each of the neighboring-cells that identifies the neighboringcell or cells that have been least-visited as compared to thecurrently-visited cell. The triggering event would cause the receivingsystem 20 to issue a control signal to the robotic device 100 thatcauses the robotic device 100 to move from the currently-visited cell tothe neighboring cell that has been visited least, e.g., by implementingone or more basic maneuvers as described herein. If two or moreneighboring cells have been visited least, the control signal wouldcause the robotic device to move from the currently-visited cell to theleast visited neighboring cell that is most compatible with the currenttravel vector of the robotic device 100, e.g., minimum travel distance.

Using FIG. 4 as an example wherein “C_(V)” identifies thecurrently-visited cell and “C_(C)” identifies the eight (8) cellscontiguous to or neighboring the currently-visited cell C_(V), theneighboring cells C_(C) that have been visited a single time are theleast-visited neighboring cells Cc. If the current travel vector for therobotic device 100 is indicated by the reference characters TV, thecontrol signal would cause the robotic device 100 to continue moving ina straight line, i.e., the move forward basic maneuver (or theStraight-Line behavioral mode) would be executed by the robotic device100 (if the robotic device 100 was currently operating in some otherbehavioral mode).

One representative navigation control algorithm for the ‘instantaneousposition’ of the navigational control system 10 uses elapsed time(either random or predetermined) as the predetermined triggering eventto cause the robotic device 10 to move to a predetermined position B inthe defined working environment. The microprocessor 24 is operative,upon expiration of the elapsed time (the predetermined triggeringevent), to determine the instantaneous position (hereinafter identifiedas “position A”) of the robotic device 100 as described herein. Sinceposition A is an unknown variable until the predetermined triggeringevent is realized, the prescribed conduct, i.e., the basic maneuvers,necessary to move the robotic device 100 from position A to position Bare also unknown. Once position A has been determined by thenavigational control system 10, the basic maneuvers necessary to movethe robotic device 100 from position A to position B are determinablesince both position A and position B are known variables (in terms oftheir known bearing, distance parameter pairs with respect to thereceiving subsystem 20). A determination of the basic maneuvers thatwill be implemented by the robotic device 100 can be accomplished by anyconventional computational technique.

Another exemplary navigation control algorithm for the ‘instantaneousposition’ embodiment of the navigational control system 10 is avariation of the “hot spot” navigation control algorithm for the‘position history’ embodiment of the navigational control system 10. Inthis illustrative embodiment, both position A and position B are knownvariables and accordingly, the basic maneuver(s) to move the roboticdevice 100 from position A to position B are known. In this example, thepredetermined triggering event is a TRUE determination that theinstantaneous position of the robotic device 100 is equal to position A(position A may be stored in memory 28 as a “zone”—defining somearbitrary area centered about position A—rather than a single pointposition to increase the probability that the instantaneous position ofthe robotic device 100 at some time will equal position A).

The receiving subsystem 20 comprises a set of detection units 30 _(M)where M is an integer defining the number of individual detection unitscomprising the set for the navigational control system 10. The numberand positioning of the set of detection units 30 _(M) should be suchthat as much of the defined working area as possible is within thefield-of-view of the receiving subsystem 20 and that the fields-of-viewof at least two (but preferably more) detection units 30M cover the samearea within the defined working area.

In preferred embodiments of the navigational control system 10 accordingto the present invention, the receiving subsystem 20 functions as a“base station” for the system 10. In this functional role, the receivingsubsystem 20 is a portable, standalone unit that is stationarilypositioned within the defined working area, preferably abutting a wallbounding the defined working area (the ‘wall unit’ configuration).Alternatively, the receiving subsystem 20 can be positioned within thedefined working area distally of the walls bounding the defined workingarea (the ‘free-standing’ configuration). The receiving subsystem 20 asthe base station establishes and, for the ‘position history’ embodimentof the navigational control system 10, stores the grid map of cellsrepresenting the defined working area and represents the origin (0, 0)of the grid map of cells described above.

For those embodiments where the receiving subsystem 20 is operated as awall unit configuration, the individual detection units 30 _(M) have aknown spaced-apart relationship and configured and operative to have a180° field-of-view. For example, FIG. 2 illustrates an embodiment of thereceiving subsystem 20 comprising two detection units 30 _(M) (M=2)spaced apart by a known angular distance “φ”. FIG. 6C illustratesanother embodiment of the receiving subsystem 20 comprising threedetection units 30 _(M) (M=3), i.e., 30 ₁₂, 30 ₂₃, 30 ₁₃, having knownangular separations identified by “φ₁₂”, “φ₂₃”, and “φ₁₃”, respectively.Preferred embodiments of the wall unit configuration for thenavigational control system 10 include three detection units 30 _(M) toprovide absolute bearing data to the robotic device 100. A minimum oftwo detection units 30M are required to provide the necessary signalinformation for the receiving subsystem 20. More than three detectionunits 30 _(M) can be employed to increase the resolution of thereceiving subsystem 20, but at an added cost for each additionaldetection unit 30 _(M) and associated signal processing circuitry (seeFIG. 6C which illustrates the representative signal processing circuitryassociated with a detection unit 30 _(M)).

For those embodiments where the receiving subsystem 20 is operated as afree-standing configuration, the individual detection units 30 _(M)likewise spaced apart by known angular distances and configured andoperative have a field-of-view greater than 180°. A representativeembodiment of the receiving subsystem 20 operated as a free-standingbase station would comprise four detection units 30 _(M).

The detection units 30 _(M) are configured and operative to detect aparameter of one or more of the directed beams emitted by thetransmitting units 14 _(N), e.g., voltages V representing the relativesignal strengths of the detected directed beam(s). In a preferredembodiment, each detection unit 30 _(M) is configured and operative toaverage the detected signal strength parameter (e.g., voltage) when thedetection unit 30 _(M) detects two directed beams simultaneously. Thereceiving subsystem 20 executes a signal processing algorithm thatprocesses the detected parameters provided by the detection units 30M,i.e., relative signal strengths of the detected beams, utilizing aconventional technique to determine the absolute bearing between therobotic device 100 and the receiving subsystem 20.

To provide the distance determination capability for the receivingsubsystem 20, the receiving subsystem 20 is preferably calibrated priorto use. This involves positioning the robotic device 100 at apredetermined distance from the receiving subsystem 20 and operating one(or more) of the transmitting units 14 _(N) to emit a directed beam atthe receiving subsystem 20. The parameter of the directed beam detectedby the detection units 30 _(M), e.g., a voltage representing the signalstrength of the directed beam as detected, is correlated to thepredetermined distance and used to generate a look-up table of signalstrength versus distance for the defined working area. This look-uptable is stored in the memory module 28 of the receiving subsystem 20.As the signal strengths of directed beams are detected during operationof the navigational control system 10, the receiving subsystem 20 usesthe detected signal strengths as pointers to the stored look-up table todetermine the corresponding distances (between the receiving subsystem20 and the robotic device 100).

Alternatively, the receiving subsystem 20 could be configured andoperative to implement a signal processing algorithm that utilizes theknown attenuation characteristics, i.e., signal strength versusdistance, of the operating frequency of the directed beams emitted bythe transmitting units 14 _(N). This embodiment presupposes that thetransmitting units 14 _(N) are rated and emitting directed beams ofknown signal strength.

For the sophisticated embodiment of the navigational control system 10according to the present invention described above wherein theindividual transmitting units 14 _(N) of the transmitting subsystem 12are operated at a unique operating frequency, the detection units 30_(M) of the receiving subsystem 20 are configured to scan the set ofunique operating frequencies utilized by the transmitting units 14 _(N).The receiving subsystem 20 is configured and operative to cause thedetection units 30 _(M) to sequentially scan through these frequenciesduring operation of the navigational control system 10.

For the innovative embodiment of the transmitting subsystem 12 describedabove in connection with FIG. 5A, FIG. 5B illustrates the operatingcharacteristics of the complementary receiving subsystem 20. Thereceiving subsystem 20 is configured and operative to detect thedirected beams emitted during the predetermined synchronization periodt_(SY). At the end of the predetermined synchronization period t_(SY),the receiving subsystem 20 is operative to initiate the timing sequencet₀. The receiving subsystem 20 is operative to detect the directed beamsas described herein. However, the receiving subsystem 20 is furtheroperative to determine the time at which the peak signal strength isdetected, see reference character t_(peak) in FIG. 5B. The receivingsubsystem 20 is further operative to correlate the peak signal strengthdetection time t_(peak) with the known times at which the signalstrength of the directed beam emitted by each transmitting unit 14 _(N)reached its peak to identify the specific transmitting unit 14 _(N) thattransmitted the directed beam detected as having the peak signalstrength (for the descriptive example presented in FIGS. 5A, 5B, thethird transmitting unit 14 ₃).

For the innovative embodiment of the transmitting subsystem 12 describedabove in connection with FIG. 5C, FIG. 5D illustrates the operatingcharacteristics of the complementary receiving subsystem 20. Thereceiving subsystem 20 is configured and operative to detect thedirected beams emitted during the predetermined synchronization periodt_(SY). At the end of the predetermined synchronization period t_(SY),the receiving subsystem 20 is operative to initiate the timing sequencet₀. The receiving subsystem 20 is operative to detect the directed beamsas described herein (as exemplarily illustrated by the detected signalpulses DP₁, DP₂, DP₃, DP₄ in FIG. 5D). However, the receiving subsystem20 is further operative to determine the two highest peak signalstrengths of the detected directed beams, see reference characters DP₃and DP₂ in FIG. 5D, which depict the highest and next highest detectedsignal pulses, and the times at which the two highest strength signalswere detected (t₂₁ and t₃₁ in FIG. 5D).

The signal strength detection times allows the particular transmittingunits 14 _(N) on the robotic device 100 to be identified, i.e.,transmitting units 14 ₃ and 14 ₂ in the example of FIG. 5D. Thereceiving subsystem 20 is then further operative to compute theamplitude ratio of these signal pulses, e.g., DP₃/DP₂, and to use suchcomputed amplitude ratio as a pointer to a look-up table that identifiesthe angular orientation of the identified transmitting units 14 ₃, 14 ₂,which in turn establishes the travel vector for the robotic device 100.

Even though the transmitting units 14 _(N) mounted in combination withthe robotic device 100 are interchangeable, the specific location ofeach individual transmitting unit 14N on the robotic device 100 is aknown quantity. Based upon the identification of the transmitting unit14N that emitted the directed beam detected by the receiving subsystem20, the receiving subsystem 20 can execute rather straightforwardgeometric calculations, based upon the location of the identifiedtransmitting unit 14N, to determine the travel vector of the roboticdevice 100.

When the receiving subsystem 20 functions as the base station, a meansis required to communicate the control signal to the robotic device.Accordingly, embodiments of the receiving subsystem 20 that operate as abase station further include a transmitting unit 32 (see FIG. 3). Oncethe navigation control algorithm implemented by the microprocessor 24has determined the prescribed conduct to be implemented by the roboticdevice 10, the microprocessor 24 is operative to select the appropriatecontrol signal to implement such prescribed conduct from the memorymodule 28. The microprocessor 24 is then operative to activate thetransmitting unit 32 to communicate (by transmitting) the control signalto the receiver unit 16 of the robotic device 100 where the prescribedconduct defined by the control signal is implemented by means of themicroprocessing unit 135.

While the robotic device 100 is described (and depicted in FIG. 3) asbeing configured to include a dedicated receiver unit 16 for receivingcontrol signals transmitted by the transmitting unit 32 of the receivingunit 20, it is preferable that the omnidirectional detector 128 (of thevirtual wall detection system) be adapted to detect and process suchcontrol signals. For those embodiments of the navigational controlsystem 10 according to the present invention wherein the receiving unit20 is integrated in combination with the robotic device 10, thetransmitting unit 32 is not required. Rather, the receiving unit 20 ofthe navigation control system 100 is electrically coupled to themicroprocessing unit 135 (via an I/O port) of the robotic device 100 sothat the receiving unit 20 can communicate control signals directly tothe microprocessing unit 135.

As disclosed above, in preferred embodiments of the navigational controlsystem 10 according to the present invention, the receiving subsystem 20functions as the base station, i.e., the wall unit configuration, andthe transmitting subsystem 12 is integrated in combination with therobotic device 100. One preferred embodiment that is illustrative of thefeatures and functionality of the navigational control system 10according to the present invention is exemplarily illustrated in FIGS.6A-6C.

FIG. 6A depicts a robotic device 100 operating in a defined working areaWA bounded by walls W. A virtual wall unit VWU is positioned in the onlyentryway to the working area WA and operative to emit a confinement beamCB that confines the robotic device 100 to operations within the workingarea WA.

The transmitting subsystem 12 of the illustrated embodiment of thenavigational control system 10 is integrated in combination with therobotic device 100 and comprises a set of transmitting units 14 _(N)(eight (8) for the described embodiment such that N equals the integers1-8) that are operative to generate a corresponding set of directedbeams DB_(N) (where N equals the integers 1-8) as illustrated in FIG. 5B(only two directed beams DB₃, DB₄ are illustrated in FIG. 5B). Referencecharacters BA₁-BA₈ identify the propagation axes of the directed beamsDB_(N) emitted by the transmitting units 14 ₁-14 ₈, respectively. Eachtransmitting unit 14 _(N) is configured and operative to emit a directedbeam DB_(N) having a predetermined emission pattern θ_(N) centered aboutthe corresponding beam axis BA_(N). For the illustrated embodiment, theemission pattern θ_(N) of each directed beam DB_(N) is approximately100°.

Preferably, the predetermined emission pattern θ_(N) of the directedbeams DB_(N) is correlated with the number of transmitting units 14 _(N)so that the transmitting subsystem 12 of the navigational control system10 emulates an omnidirectional transmitting source. An omnidirectionaltransmitting source is necessary to ensure that one or more of thedirected beams DB_(N) are detected by the receiving subsystem 20 sincethe position and orientation of the robotic device 100 in the definedworking area (e.g., in terms of its forward motion FM), with respect tothe receiving station 20, is an unknown variable at any particularmoment in time. Preferably the emission patterns θ_(N) of the directedbeams DB_(N) overlap.

As an examination of FIGS. 6A, 6B (and in particular FIG. 6B) shows, thedirected beams DB₃, DB₄ emitted by transmitting units 14 ₃, 14 ₄,respectively, will be detected by the detection units 30 ₁, 30 ₂, 30 ₃of the receiving subsystem 20. The detection units 30 ₁, 30 ₂, 30 ₃ areoperative to detect a parameter representative of the relative signalstrengths of the detected beams DB₃, DB₄, e.g., V1, V2, V3, respectively(as disclosed above each detection unit 30N is operative to average thesignal strengths when two directed beams are detected simultaneously).

The receiving subsystem 20 is operative to implement the signalprocessing algorithm to compute the absolute bearing and distancebetween the receiving subsystem 20 and the robotic device 100. Thereceiving subsystem 20 then implements the navigation control algorithmto correlate the computed bearing and distance with one of the cellscomprising the grid map of the defined working area WA stored in thememory module 28, and adds such cell to the position history of therobotic device 100 to update the position history. The receivingsubsystem 20 is then operative under the navigation control algorithm todetermine if there is a predetermined triggering event associated withthis updated position history. If so, the receiving subsystem 20 isoperative to select the appropriate control signal, as determined by thenavigation control algorithm, and transmit such control signal to thereceiver unit 16 of the robotic device 100 using the transmitting system32 (see FIG. 3). The microprocessing unit 135 of the robotic device 100,is operative in response to the reception of the control signal by meansof the omnidirectional detector 128, to implement prescribed conduct,e.g., one or more of the basic maneuvers and/or behavioral modesexemplarily described herein, specified by the control signal.

An exemplary embodiment of a navigational control system 10′ accordingto the present invention wherein the transmitting subsystem 12 functionsas a base station and the receiving subsystem 20 is integrated incombination with the robotic device 100 is illustrated in FIG. 7. Thetransmitting subsystem 12 comprises a distributed set of transmittingunits 14N positioned to abut the walls W of the defined working area. Asillustrated in FIG. 7, the transmitting subsystem 12 comprises a firsttransmitting unit 14 ₁, a second transmitting unit 14 ₂, and a thirdtransmitting unit 14 ₃ positioned in abutting engagement with adjacentwalls W, respectively.

Each transmitting unit 14N comprising this distributed set is configuredand operative to emit a directed beam having a predetermined emissionpattern θ_(N) along a predetermined beam axis DB_(N) (DB₁, DB₂, and DB₃in FIG. 7 define the predetermined beam axes for the distributedtransmitting units 14 ₁, 14 ₂, 14 ₃, respectively) at a unique operatingfrequency, preferably in the infrared frequency range and preferablymodulated as disclosed herein. Preferably, each transmitting unit 14 ₁,14 ₂, 14 ₃ is configured and operative to generate a predetermined beamemission pattern θ_(N) that effectively covers the defined working areaWA, i.e., θ_(N) is approximately 180° for the distributed transmissionsubsystem 12 depicted in FIG. 7.

The receiving subsystem 20 for the navigational control system 10′preferably comprises a single omnidirectional detection unit 30 whichmay be of the type described in commonly-owned, co-pending U.S. patentapplication Ser. No. 10/056,804, filed 24 Jan. 2002, entitled METHOD ANDSYSTEM FOR ROBOT LOCALIZATION AND CONFINEMENT (the virtual wall systemsummarily described herein). The omnidirectional detection unit 30 isconfigured and operative to scan through the unique operatingfrequencies utilized by the distributed transmitting units 14 ₁, 14 ₂,14 ₃.

The omnidirectional detection unit 30 is operative to detect thedirected beams DB1, DB2, DB3 emitted by the distributed transmittingunits 14 ₁, 14 ₂, 14 ₃. The receiving subsystem is configured andoperative to process the signals of the detected directed beam todetermine the absolute position of the robotic device 100 within thedefined working area WA. This absolute position is defined in terms of acell of the grid map of the defined working area WA. A sequence ofabsolute positions, determined as described above, identifies a sequenceof cells that defines the position history of the robotic device 100.

The receiver subsystem 20 is operative as described above to utilize anavigation control algorithm to determine whether a triggering event hasoccurred in the position history, and if a trigger event has occurred,the receiver subsystem 20 is operative to communicate the control signalassociated with the triggering event/navigation control algorithm to therobotic device 100. The robotic device 100 is operative, in response tothe communicated control signal, to implement the prescribed conductspecified by the control signal.

A variety of modifications and variations of the present invention arepossible in light of the above teachings. The navigational controlsystem 10 according to the present invention has been described above asdetermining and using the instantaneous position (or a sequence ofinstantaneous positions) of a robotic device as a control parameter fordirectly altering the movement activity of the robotic device. Oneskilled in the art will appreciate that the navigational control systemaccording to the present invention can be used for other purposes. Forexample, the navigational control system of the present invention can beused for correcting errors in movement activity of robotic devicesrelying upon dead reckoning. It is therefore to be understood that,within the scope of the appended claims, the present invention may bepracticed other than as specifically described herein.

What is claimed is:
 1. A robotic cleaner, comprising: a chassis and anouter shell secured to the chassis; left and right main drive wheelassemblies and respective independent electric motors, independentlymounted in pivotally-biased combination with the chassis for pivotalmotion with respect thereto at opposed ends of the transverse diameterof the chassis, and movable between a retracted position under theweight of the robotic cleaner during operation and an extended positionwherein their axes of rotation are below the bottom plane of thechassis; a navigational control system operative to monitor movementactivity of the robotic cleaner within a defined working area, themonitored movement activity including at least one of a position historyof the robotic cleaner and an instantaneous position of the roboticcleaner; and a transmitting subsystem including a mechanical sweepingtransmitter laser, wherein the mechanical sweeping transmitter laser: isconfigured to sweep to redirect a transmitting element of the mechanicalsweeping transmitter laser; is configured to transmit in the infraredrange from about 750 nm to about 1.4 ×10^4 nm; is configured to coverthe defined working area by transmitting a beam substantially parallelto a surface of the defined working area; is mounted in combination withthe outer shell secured to the chassis to define an overall structuralenvelope of a height to enable movement of the robotic cleaner underfurniture; and is integrated in combination with a high point of ahousing infrastructure of the robotic cleaner so that none of thestructural features of the robotic cleaner interfere with sweeping ofthe transmitting element of the mechanical sweeping transmitter laser.2. The robotic cleaner of claim 1, further comprising a receiver unitconfigured to receive control signals.
 3. The robotic cleaner of claim1, wherein the navigational control system is configured to create atessellation of the defined working area by segmenting the definedworking area into a set of individual cells.
 4. The robotic cleaner ofclaim 3, wherein the navigational control system is configured to definea size of each individual cell based on a width of a cleaning headsystem of the robotic cleaner.
 5. The robotic cleaner of claim 1,further comprising a rechargeable battery pack integrated in combinationwith the chassis.
 6. The robotic cleaner of claim 1, further comprisinga forward bumper integrated in movable combination with the chassis,wherein the forward bumper is configured so that when the chassisencounters an obstacle, the bumper is displaced towards the chassis andreturns to an extended position when contact with the obstacle isterminated.
 7. The robotic cleaner of claim 1, further comprising awheel drop sensor integrated in combination with each of the main drivewheel assemblies and operative to generate a signal whenever any of thewheel assemblies is in an extended position in which the axes ofrotation thereof is below the bottom plane of the chassis.
 8. Therobotic cleaner of claim 1, further comprising an obstacle-followingunit comprising an IR emitter—detector pair configured to transmit asignal to a control module if reflected radiation is not detected by thedetector.
 9. The robotic cleaner of claim 1, further comprisingrespective stall-sensor units integrated in combination with eachrespective independent electric motor and operative to transmit a signalto the control module when a change in current is detected in therespective independent electric motor.
 10. The robotic cleaner of claim1, further comprising at least one cliff detection unit comprising an IRemitter—detector pair configured to transmit a signal to the controlmodule when a drop-off is encountered.
 11. The robotic cleaner of claim1, wherein the mechanical sweeping transmitter laser is configured tocycle on/off sequentially.